1. Field of the Invention
This invention relates to the production of useful adsorbents from spent oil bleaching adsorbents.
2. Brief Description of Related Art
The bleaching of vegetable or mineral oils by treating them with particulate adsorbent material is practised on a large scale and gives rise to considerable residue disposal problems. Spent adsorbent usually contains from about 20% to about 40% by weight of residual oil, and may give rise to the hazard of spontaneous ignition in contact with air, particularly if the adsorbed oil is an unsaturated one. Dumping of this material may therefore be practised only under quite rigorous precautions. There exist a variety of methods for extraction of some or all of the adsorbed oil, such as treating with hot water containing a surface active agent, which may reduce the content of adsorbed oil to as little as about 5% by weight but produces a water phase which requires work-up to separate the oil in re-usable form. Organic solvent extraction processes are also available but are subject to the need to take stringent precautions for environmental and operator protection from solvent emissions.
A variety of adsorbents may be used to bleach oils for example activated charcoal, silica gel, alumina, and bleaching earths such as fuller's earth, kaolinite, attapulgite or montmorillonites. Apart from activated charcoal these materials do not have any particularly high activity in relation to the removal of many aromatic impurities from oils although they may be effective to various degrees in reducing the content of colour bodies in the oil. The impurities referred to may be simple aromatic molecules such as phenols or they may be polyaromatic hydrocarbons which may be present in fish oil and in certain vegetable oils such as coconut oil and rapeseed oil. Certain polyaromatic hydrocarbons, such as benz(a)pyrene, are known or suspected carcinogens and it is desirable to remove these compounds and other aromatic materials from oils intended for consumption and from organic or aqueous wastes or effluents.
It has previously been proposed in Polish Patent Specification No. 107835 to produce adsorbents from spent bleaching earths or zeolites which are coated with organic compounds having a high content of carbon, such as an oil, by treating them with a mineral acid carbonising agent at a temperature of from 0.degree. C. to 250.degree. C. A wide variety of uses is postulated for the adsorbents so obtained although no demonstration of effectiveness for any use is described in the specification. The products obtained from a repetition of the teaching of this patent were found to be of poor physical form and to have no adsorptive effect in relation to aromatic hydrocarbons.